第一节：单项填空（共20小题；每小题1分，满分20分）
21. As _____ birthplace of Huaxia civilization, Xi'an is_____city with a long history and abundant cultural relics .
A. the ; a B. a ; a C. / ; a D the ; /
22. H7N9 control and prevention is a_____ to China as well as the whole world.
A.surprise B. challenge C reaction D. threat
23. My boss made _____ clear that one in three of us will have to leave next month. A.it B.us C. that D. this
24. — Have you seen John lately?
— Yes, he comes to visit me ______?
A. the other day B. now and then
C. at the moment D. sooner or later
25.Hearing the news about Neil Armstrong”s death ,______.
A. my heart missed a beat B.my mind went empty
C. the newspaper shook with my hands D. I was greatly shocked
26．He serves the public wholeheartedly, ______ his personal gain or loss．
A．in reference of B．owing to C．in terms of D．regardless of
27. ______you are what you eat, you should eat healthily.
A. Unless B. Although C. Since D.While
